It is known in the art relating to spark ignited gasoline engines, particularly those for automotive use, to provide means for heating the intake air-fuel mixture with heat transferred from the engine exhaust gases. Among the arrangements proposed and utilized for this purpose are included those having juxtaposed intake and exhaust manifolds with interrelated passages wherein exhaust gases are directed against a plate or wall to which the intake manifold mixture is exposed, preferably at a point below the manifold inlet and the throat of the associated carburetor. The heating of the plate or wall by the exhaust gases vaporizes fuel droplets impinging on the wall or plate and heats the adjacent air-fuel mixture. To control systems of this type, thermostatic or time controlled valves are often used to direct exhaust gases toward or away from the plate or wall to provide maximum exhaust heat during engine warm up and afterwards limit the amount of heat transferred to some lesser amount.
To overcome some of the problems inherent in mechanical valve systems, it has been proposed to use two-phase thermosyphons, more recently known as heat pipes, in which a vaporizable fluid is utilized to transfer heat from the exhaust gases to a fuel vaporizing chamber. However, some of the systems proposed have involved relatively complex arrangements for vaporizing the fuel in advance of mixing with the main air charge and would appear not to obtain the desired advantages of simplicity and practicality along with the fast warm up and automatic temperature regulation desired of such systems.